Great advances in the field of wireless communications have been made over the past ten to twenty years, and continue to be made. These advances both improve the quality of communication, e.g., the clarity and reliability of communication, and improve the geographic coverage of such wireless communications. As industry strives to provide a wireless communications capability that covers the entire globe, factors such as economic viability dictate that space-based transceivers be employed to compliment ground infrastructure. Ground infrastructure remains technologically advantageous and economically preferable in identified population centers where a great deal of bandwidth is required in a relatively small area. However, satellites can provide universal coverage economically extending coverage over less populated areas. Thus, two types of wireless communication, i.e., ground infrastructure cellular, and space-based satellite systems have emerged. One of the most ubiquitous terrestrial cellular systems is the Global System for Mobile Communications (GSM). Geo Mobile Radio (GMR-1) is an example of systems which are extensions of GSM to the mobile satellite communication system venue.
In both types wireless communication systems, there are physical channels and logical channels. A physical channel in GSM or GMR-1 is a continuous allocation of resources including both a frequency and a time component. The frequency is given by an absolute radio frequency channel number (ARFCN) allocation, and the time component is given by the allocated time slot(s) within a frame. Logical channels are mapped to physical channels. Logical air interface channels of interest include: broadcast control channel (BCCH) 5 (from network to a user access terminal or forward direction); random access channel (RACH) 19 (from user access terminal to network or return direction); and access grant channel (AGCH) 21 (forward direction). The network uses logical channels to convey signaling and control message. For example, system information messages are conveyed on the BCCH 5, channel request messages are conveyed on the RACH 19 and immediate assignment reject and immediate assignment messages are conveyed on the AGCH 21. Messages contain information elements and information elements can have many different values.
FIG. 1 illustrates a block diagram of a satellite communication system according to the prior art. A satellite communications network, such as a geo-synchronous earth orbit mobile communications network, comprises at least one geo-synchronous earth orbit satellite 6, a ground-based resource manager (RM) 16 and spacecraft operations center (SOC), associated with satellite 6, at least one ground-based existing gateway station (EGW) 8, and at least one user access terminal 20, which is typically a hand-held or vehicle mounted mobile telephone. Satellite 6 enables access terminal 20 to communicate with other access terminals 20 or with other telephones in a terrestrial network (for example, a public switched telephone network or PSTN), via the gateway stations. RM 16 provides system-wide resource management, and the SOC controls on-orbit satellite operations for its respective satellite 6. A system may comprise one or more satellites 6.
In a terrestrial cellular system an antenna's coverage area (both receive and transmit) is known as a cell. The equivalent concept in a mobile satellite system is a spot beam. The spot beam is defined as the coverage area of a satellite antenna or antenna subsystem, which may consist of a phased an-ay or a multiplicity of antenna elements with or without a reflector. The typical mobile satellite may have hundreds of spot beams. A “cell” or “spot beam” is defined to exist independent of whether or not it is actually radiating or receiving energy at the time. Thus, we can define an illuminated spot beam as a beam into which energy is actually being radiated by the antenna and a dark spot beam as a beam in which the satellite's antenna is not radiating any energy or a signal. More specifically, the transmission of BCCH 5 into the cell or spot beam is required.
The spot beam in FIG. 1 shall be referred to as spot beam 10. BCCH 5 contains the system information necessary for access terminal 20 to receive so that it can be aware of the cell or spot beam's 10 existence. In GSM cellular technology specifications an access terminal is referred to as a “mobile station” (MS). In the GMR-1 mobile satellite specifications an access terminal is referred to as a “mobile earth station” (MES). For generality, the term “access terminal” 20 will be used in this document
The system information messages broadcast by the network on the BCCH 5 contain the information necessary for access terminal 20 (as shown in FIG. 1) to determine where the RACH 19 and AGCH 21 channels are (timeslots and ARFCNs) and any rules governing the use of the RACH 19 channel by access terminal 20. In GSM and GMR-1, RACH 19 channels and AGCH 21 channels are paired so that an access terminal's channel request message on a specific RACH 19 will always be responded to by an immediate assignment or immediate assignment reject message from the network on the specific paired AGCH 21. The system information messages broadcast on the BCCH 5 channel also contain information elements which describe the service provider bearer services which are offered to access terminal 20 within the spot beam or cell. A GMR-1 BCCH 5 also contains a concurrent BCCH list, which is a list of BCCHs 5 being broadcast into the same spot beam 10 by the network and their services and service providers. Except for the concurrent BCCH list, all of this information or its equivalent exists in GSM. All of the information which the terminal needs to know in order to operate within the system is contained in the system information messages.
GMR-1 05.005 and GSM 05.05 partition the radio frequency spectrum available to the air interface into radio frequency channels, and defines an ARFCN for each channel. Each spot beam in GMR-1 (or cell in GSM) is allocated a subset of these channels. These channels process are defined as the beam allocation. One radio frequency channel of the beam allocation is used by the network to broadcast the BCCH and is known as the BCCH carrier.
GSM and GMR-1 use time division multiplexing (TDMA). Time is partitioned into TDMA frames and timeslots as defined in GMR-1 05.002 and GSM 05.02. The transmissions within these timeslots are known as bursts. A burst is a single unit of transmission on the radio path defined in terms of center frequency (or ARFCN), bandwidth, power profile, and duration (in numbers of contiguous timeslots).
Logical channels are mapped to physical channels by a set of multiplexing rules. They can be statically or dynamically mapped to physical channels. These rules are defined in GSM 05.02 for GSM and GMR-1 05.002 for GMR-1.
At present, the typical mobile communications satellites are non-processing satellites or bent-pipe satellites. That means that all physical bursts are transmitted or originated by a ground-based transmitter, either an access terminal 20, EGW 8 or new gateway (NGW) 12, and these are received and retransmitted by the satellite. Satellite 6 does not initiate transmission or originate physical bursts. Typically, there is a radio frequency spectrum allocated to the link between access terminal 20 and satellite 6 and another radio frequency spectrum allocated to the feeder link between satellite 6 and EGW 8. If EGW 8 transmits a burst on the feeder link, satellite 6 receives the burst and performs a frequency translation from the feeder link frequency to an appropriately allocated ARFCN and retransmits the burst on the forward link ARFCN into spot beam 10. If no feeder link burst is present satellite 6 has no signal to retransmit. Also, if access terminal 20 transmits a burst on an appropriately allocated ARFCN return link, satellite 6 receives the burst and performs a frequency translation to the appropriately allocated feeder link frequency and retransmits the burst from access terminal's 20 signal to EGW 8.
When an access terminal 20 is turned on or powered up it searches for a BCCH 5 broadcast in a spot beam 10. Since there can be hundreds of spot beams 10, the access terminal 20 must perform a task called spot beam selection. Spot beam selection in GMR-1 is described in GMR-1 specifications 03.022 and 05.008 and in U.S. Pat. No. 6,233,451, “SPOT BEAM SELECTION IN A MOBILE SATELLITE COMMUNICATION SYSTEM”, (the entire contents of which are expressly incorporated herein by reference). Spot beam selection is the selecting of a BCCH carrier to “camp-on”, which combines comparison and selection based on received signal strengths of BCCH carriers with a comparison and selection based on service provider or PLMN identity. Briefly, In GSM, access terminal 20 measures the power in all the BCCH carriers and selects all the ones with received signal strengths greater than some criteria and creates a rank-ordered list. The access terminal 20 then reads the system information broadcast on the BCCHs 5 of the BCCH carriers in the rank-ordered list and selects the one, which has a preferred service provider or PLMN. This is often not the closest cell or the strongest signal.
In GMR-1, in order to conserve satellite power and access terminal 20 power during communications, it is important that the access terminal 20 always select the correct spot beam. To assist the access terminal 20, two lists are broadcast in the system information of each BCCH 5, the neighbor list and the concurrent BCCH list. The neighbor list is a list of BCCH carriers used in the adjoining spot beams 10. The access terminal 20 makes measurements of these neighbors for signal strength comparison. The concurrent BCCH list is a list of all BCCH carriers in the same spot beam. These may be from a different EGW 8 or NGW 12. The concurrent BCCH List includes the PLMN ID, which is the service provider identity of the operator of the system broadcasting the concurrent BCCH. The PLMN ID is referred to as the “public land mobile network identifier” and it is composed of a mobile country code (MCC), and a mobile network code (MNC). The access terminal 20 avoids measurement comparison of concurrent BCCH carriers to make a spot beam selection, however once the access terminal 20 selects a spot beam 10, it compares PLMN identities of each BCCH 5 on the concurrent list and “camps-on” the BCCH carrier with a preferred PLMN.
As a further innovation of GMR-1, the access terminal 20 has incorporated a Global Positioning System (GPS) receiver. The system information message in the BCCH 5 also contains the latitude and longitude of the spot beam 10 center. Access terminal 20 may optionally compare its GPS position to the spot beam center position to accurately determine the correct spot beam. Since access terminal 20 is required to report this position in the channel request message, the network may optionally redirect the access terminal 20 to a different spot beam 10 based on a comparison of the reported access terminal 20 position and the coverage area map of all spot beams 10.
In order to support ubiquitous service throughout the satellite's coverage area, a gateway (EGW 8 or NGW 12) must broadcast a BCCH (BCCH 5 and BCCH 5′, respectively) into every existing spot beam 10. This means that the RM 16 must allocate at least one BCCH 5 carrier for each spot beam 10 for use by the gateway RM 16. Further, satellite power must be allocated for each spot beam 10 to be illuminated by the gateway with a BCCH 5 (or BCCH 5′) transmission.
Having selected a spot beam 10 and a BCCH carrier, the access terminal 20 must transmit a channel request message on the RACH 19 (or RACH 19) channel to request a traffic channel for communication of user data and/or signaling. Prior to transmitting this message, however, the access terminal 20 must make one more check. It must read the cell-bar-access bit in the system information to determine if access terminals are barred from attempting access to the cell or spot beam. If this bit is ‘1’ access is barred and if the bit is ‘0’ access is permitted. In the case assess is permitted, the access terminal 20 would request a channel with the establishment cause “to register”. The definition of the cell bar access bit is shown in Table 1. If the user subsequently wanted to make a phone call, the access terminal 20 would request a channel for that purpose with establishment cause “to originate a call”. Alternatively, someone in the PSTN might call the user, in which case, having registered with the network. the network knows the location, cell or spot beam and can page the access terminal. Upon receiving a page, the access terminal 20 transmits a channel request message with establishment cause “responding to a page.” Other establishment causes exist.
TABLE ICell Bar AccessAny Service1Barred0Not Barred
In the prior art of GSM and other cellular and mobile satellite systems, the channel request message typically only contains a random reference and an establishment cause. A random reference is a unique random number generated by access terminal 20 and passed to the gateway within the RACH message, and which uniquely identifies that access terminal 20. It is used by the gateway to address access terminal 20 when sending the immediate assignment or immediate assignment reject message to access terminal 20 on the AGCH 21 (or AGCH 21′). This is used in the event of contention, between a first and second (or any number of) access terminals 20. As we have seen, the establishment cause tells the gateway the reason the access terminal 20 is requesting a channel (i.e., the reason to “establish” a channel). An innovation, introduced in the prior art of GMR-1, is for the channel request message to contain much more detailed information about the establishment cause and the requesting access terminal 20. The GMR-1 channel request message contains, in addition to the establishment cause and random reference, the SP/HPLMN ID (Service Provider/Home Public Land Mobile Network), the called party number, the GPS-derived position of the access terminal 20 and other information elements. The network reads all of these information elements and determines the disposition of the channel request message from access terminal 20. Any of the values of these information elements may trigger existing gateway (EGW) 8 to process access terminal's 20 request for access in a specific way, such as setting up a terminal-to-terminal call (described in GMR-1 specification 03.096) or optimally routing the call to another EGW 8 (described in GMR-1 specification 03.097) or rejecting the call based on geographic location, (described in GMR-1 specification 03.099) etc. None of these services are offered in GSM and there is no comparable specification.
U.S. Pat. No. 6,249,677, (the entire contents of which are herein incorporated by reference), is entitled “Apparatus and Method for Delivering Key Information of a Channel Request Message From a User Terminal to a Network” and discloses an apparatus and method, for use with the satellite-based communications network, for improving the reliability and speed at which communication between a user terminal and the network is established. The apparatus and method arranges data of a channel request message transmitted from a user terminal to a satellite in the satellite-based network to insure that the most critical data for establishing communication between the user terminal and the satellite-based network is received at the satellite during the appropriate receiving time frame window. The channel request message includes a first data group necessary for establishing a communication link for which information is transmitted between the apparatus and the network, and a second data group including information for decreasing the amount time necessary to establish the communication link. The first data group is positioned at the center of the Channel Request Message, with portions of the second data group at opposite ends of the Channel Request Message. The time at which the user terminal transmits the Channel Request Message is set based on a location of the apparatus within a spot beam, to take into account the appropriate propagation delay time for the message to travel from the apparatus to the satellite in the network, thus assuring that at least the first data group of the Channel Request Message is received at the satellite during an appropriate receiving time frame window.
FIG. 2 illustrates a message flow diagram showing the establishment of a communications channel between an access terminal and the network according to the prior art. As discussed above, EGW 8 continuously transmits BCCH 5 (step 202), which contains system information messages. In step 204, access terminal 20 “camps on” BCCH 5, and retrieves the critical system information. Included in this system information is the frequency identity of the RACH 19 channel which access terminal 20 may use to communicate with EGW 8. For example, access terminal may transmit a channel request message to EGW 8 in order to access existing services. Upon receiving the channel request message from the access terminal 20 on the RACH 19 (step 206) the network responds with either an immediate assignment or an immediate assignment reject message on the AGCH 21 (step 204). Communication on a traffic channel may then begin, as shown in step 210.
As described, in order to offer wireless mobile service, a network or system must advertise its presence and capabilities via system information messages broadcast on the BCCH 5. This broadcast costs resources to a service provider. These resources include spectrum, power as well as radio equipment. When there are two gateway stations serving the same spot beam 10, each gateway stations must use an RF carrier as the BCCH carrier and each gateway station must broadcast the BCCH 5 continuously, in order for the access terminal 20 to discover and read the system information on the BCCH 5 and access services (step 210) from the gateway. Both gateways must illuminate their BCCH carriers.
A new service provider or the existing service provider, launching a new service, is normally required to spend resources to broadcast the system information associated with the new service. In order to support ubiquitous service in the entire coverage area of the satellite system, by the prior art, the NGW 12 must broadcast a BCCH 5 in every spot beam. This requires the allocation of at least one BCCH carrier for every spot beam 10, an allocation of satellite power for every spot beam 10, and the allocation of other required system resources, such as transmitters sufficient to support the transmission of a BCCH 5 in every spot beam 10 by NGW 12. Accordingly, a need arises to allow an existing service provider, which is already providing ubiquitous service, to support by proxy a second service provider and/or a new service. Such as capability offers the opportunity to save system resources. However, a method is required, which minimizes the impact to the existing proxy network, and at the same time requires no modifications to the user access terminal 20 already using the proxy network for existing services, and minimal modifications to a new access terminal 20 and existing gateway station equipment.
FIG. 3 illustrates a state transition diagram for a GSM/GPRS mobility management software layer according to the prior art. In GPRS, GMM V.02 state machine provides two major states: GMM-Deregistered and GMM-Registered. In the design of access terminal 20, the software that controls a microprocessor, which in turn controls the transceiver and I/O functions of access terminal 20, is divided into several or more layers. Generally speaking each of these “layers” are related software code, responsible for accepting inputs (some internally generated, some externally), generating outputs (again, both internal and external) and processing received data to perform specific actions. “Layers” is a way of organizing the code, to categorize functionality to increase efficiency and economy of operation. These layers can be organized into a state transition diagram which shows expected results for specific inputs. There concepts are well known by those skilled in the art of software design. In the prior art access terminal, there is a GMM layer 301 and an RR layer 302.
A deregistered access terminal 20 will stay in a GMM-Deregistered state 302 in which access terminal 20 will not perform any routing area updates and the network will never page access terminal 20. A registered access terminal 20 will stay in GMM-Registered state 304, whereby it can initiate call/session setup, routing area update and be paged by the network. Transition between the two states are caused by events shown in FIG. 3. Implicit in all prior art systems is that spot beams always exist, and are always illuminated.
Upon power-on, GMM Layer 301 transitions from state 306 to GMM Deregistered (GMM Dereg.) PLMN Search State 308. Generally, in discussing FIG. 3, transitions from one state to another will be referred to as a “path”. Transitions from a state are described with the following nomenclature: Paths are given designations representing the state of origin. For example, a first path, “path A” originating from state 310, will be referred to as “path 310A”.
When GMM Layer 301 is in GMM Dereg. PLMN Search State 308, access terminal 20 is searching for PLMNs; generally, any BCCHs, but most probably an A-BCCH 9. At this point, access terminal 20 is not registered with any gateway, and that is why, as discussed above, GMM Layer 804 is described as being “de-registered”. In a “deregistered” state, access terminal 20 has GPRS capability enabled, but no GMM context has been established. In this state of being “deregistered” access terminal 20 may establish a GMM context by starting the GPRS attach procedure.
Eventually, a PLMN is identified, and GMM Layer 804 transitions to either GMM Dereg. Normal Service State 310, or GMM Dereg. Limited Service State 308, via paths 308A or 308D respectively. Otherwise, GMM Dereg. PLMN Search State 308 is left when it has been concluded that no cell is available at the moment, and GMM Layer 301 transitions to GMM Dereg. No Cell Available State 336, via path 308C.
GMM Dereg. Normal Service State 310 is defined as the state to wait for operator initiated registration request. In GMR-1, registration is automatic and therefore this state has no waiting period. GMM Layer 804 transitions from GMM Dereg. Normal Service State 310, through path 310A, to GMM Dereg. Attach Needed State 312.
In GMM Dereg. Attach Needed State 312, valid subscriber data is available and for some reason a GPRS attach must be performed as soon as possible. GMM Dereg. Attach Needed State 312 is usually of no duration, but can last if the access class is blocked. An access class represents a “quality of service” indicator. That it, different access classes are established (perhaps as many as 15 or more) and users may be assigned to any one of them. The user's quality of service may depend on the access class to which it belongs.
While GMM Layer 301 is in GMM Dereg. Attach Needed State 312, GMM Layer 301 sends a message to RR Layer 303 to perform an “Attach Request“procedure, and GMM Layer 301 transitions through path 312A to GMM Registered (GMM Reg.) Initiated State 316. GMM Reg. Initiated State 316 is an “in-between” state—neither de-registered as in state 302, nor registered as in state 304.
In GMM Reg. Initiated State 316, a GPRS attach procedure has been started and access terminal 20 is waiting a response from the network. There can be several outcomes to this request. First, if the attempt to attach is rejected, GMM Layer 301 transitions to GMM Dereg. Attempting to Attach State 314 via path 316A. GMM Dereg. Attempting to Attach State 314 represents the condition in which no GMM Layer 301 procedure will be initiated except a GPRS Attach. The execution of further attach procedures depends on the GPRS attach procedure counter. However, while GMM Layer 301 is in GMM Dereg. Attempting to Attach State 314, there are several other possible transitions that might also occur.
GMM “registered” defines a set of states in which a GMM context has been established, i.e. the GPRS attach procedure has been successfully performed. In these states, access terminal 20 may activate PDP contexts, send and receive user data and signaling information, and may reply to a page request. Furthermore, cell and routing area updating are performed.
GMM Registered Normal Service State 318 is the state in which user data and signaling information may be sent and received. In GMM Registered Update Needed State 320, access terminal 20 has to perform a routing area updating procedure, but its access class is not allowed in the cell. The procedure will be initiated as soon as access is granted (this might be due to a cell-reselection or due to change of the barred access class of the current cell). No GMM procedure except routing area updating shall be initiated by access terminal 20 in GMM Registered Update Needed State 320. Additionally, while in GMM Registered Update Needed State 320, no user data and no signaling information shall be sent.
After transitioning to GMM Reg. Update Needed State 320, GMM Layer 804 causes a Routing Area Update (RAU) request to be issued, and this places GMM Layer 804 in GMM Routing Area Update Initiated State 322. Note that similarly to GNM Registered Initiated State 316, GMM Routing Area Update Initiated State 322 is neither registered 304 nor deregistered 302, but, “in-between.” GMM Routing Area Update Initiated State 322 is the state in which a routing area update procedure has been stated and access terminal 20 is awaiting a response from the network.
Following the request, access terminal 20 is involved in communications with NGW 12, and enters GMM Reg. Attempting to Update State 324, via path 322A. GMM Reg. Attempting to Update State 324 may be described as the condition in which a routing area updating procedure has failed due to a missing response from the network. Similar to attach procedure, access terminal 20 retries the procedure controlled by timers and a GMPRS attempt counter. No GMM procedure except routing area updating shall be initiated by access terminal 20 while in this state. No data shall be sent or received.
GMM layer 301 may leave GMM routing area update initiate state 322 via path 322B, if the RAU is accepted or if the RAU counter is less than five (5), a failure case occurs and the current RAI equals the stored RAI. If those conditions are true, GMM Layer 804 proceeds, via path 322B, to GMM Reg. Normal Service State 318.
GMM Layer 301 may leave GMM Reg. Normal Service state 310 for several reasons. First, if n/w initiates a detach received with reattach, GMM Layer 301 transitions to GMM Dereg. Attempting To Attach State 314 via path 318B. Second, if n/w initiates a detach received without reattach implicit detach, GMM Layer 301 will transition to GMM Dereg. Normal Service State 310 via path 318C. And lastly, if access terminal originates a detach request, GMM layer 301 will transition to GMM Dereg. Initiated State 326, via path 318D. Once at GMM Dereg. Initiated State 326, GMM layer 301 will transition to GMM Dereg. Normal/Service State 310 via path 326B if the detach request is accepted.